This invention relates to devices for forwarding lead frames carrying a plurality of semiconductor pellets thereon to and from a work station at which die bonding operations, etc., are performed on the semiconductor pellets carried on the lead frames; this invention also relates to methods of operating such forwarding devices.
FIG. 1 shows in a perspective view of a conventional device for forwarding semiconductor lead frames.
Each of a pair of clamp units 1a and 1b for clamping the lead frame 7 at a side thereof, comprises an upper and a lower jaw 1c and 1d. The two units 1a and 1b are of identical structure and are connected to each other via connector rods 2. On a ball thread 3 is threaded a nut 3a to which a transmission plate 4 coupled to the clamp unit 1b is mounted. Thus, the translation of the nut 3a effected by means of the ball thread 3 is transmitted via the transmission plate 4 to the clamp units 1b and 1a. The device further comprises a rail 5 having sliding surfaces for supporting the side and the bottom surfaces of the lead frame 7 and rails 6a and 6b which are partitioned into two parts for translating the clamp units 1a and 1b in the forwarding direction of the lead frame, wherein the rail 6a is a bottom guide rail whose upper surface forms the sliding surface for the bottom surface of the lead frame 7, and the rail 6b is the side guide rail, a portion of whose surface opposing the rail 5 forms a sliding surface for a side surface of the lead frame 7. As is well known, the lead frame 7 carries a plurality of semiconductor pellets thereon at a predetermined pitch.
A heater device 8 for heating the lead frame 7, consisting for example, of a heat block, is vertically translatable and supported by a cam (not shown). Further, a lead frame presser 9, positioned above the heat block 8, is vertically translatable and supported by a cam 9a, for example, for pressing a lead frame 7 forwarded by the clamp units 1a and 1b against the upper surface of the heat block 8.
Furthermore, a threaded shaft 10 for width adjustment comprises left- and right-handed threads engaging nuts 10a and 10b of right- and left-handed threads, respectively, which are mounted to the rail 5 and the bottom and the side guide rails 6a and 6b.
The operation of the conventional device for forwarding the semiconductor lead frames is as follows.
The lead frame 7 is accommodated in a forwarding means (not shown) distinct from that shown in the figure, e.g., a magazine for lead frames, and is inserted by a pusher, for example, into the forwarding device of FIG. 1 by a predetermined length. Upon insertion, the lead frame 7 is guided by the rail 5 and the bottom and side guide rails 6a and 6b.
Next, the ball thread 3 is driven by a driving device (not shown), and the clamp unit 1b is returned, with the upper and lower jaws kept open, to the position spaced by a predetermined length to the left in the figure from the front end of the inserted lead frame 7. Thereafter, the upper and lower jaws of the clamp unit 1d are closed to clamp the lead frame 7 therebetween at one side of the lead frame. Further, the clamp unit 1b, which keeps on clamping the lead frame 7, is translated toward the right in the figure by a predetermined length, e.g., a length equal to the pitch of the lead frame 7. Next, the clamp unit 1b is opened, and the ball thread is rotated in the reverse direction to return the clamp unit 1b to the original position at which the lead frame 7 was clamped. This sequence completes one forwarding operation cycle.
Thus, by means of one forwarding operation cycle of the clamp unit 1b, the lead frame 7 is forwarded by a predetermined length, e.g., by a length equal to the pitch of the lead frame 7. In like manner, the forwarding operation cycles are repeated, thereby forwarding successively the lead frame 7 to the predetermined position of the heat block 8.
When the lead frame 7 is forwarded to the heat block 8, the lead frame presser 9 is in an upward released position. In addition, the heat block 8 is in a downward position. Next, the cams operating the heat block 8 and the pressure 9 are driven so that the heat block 8 is raised and the presser 9 is lowered. Thus, the lead frame 7 fed by the clamp unit 1b is pressed on the upper surface of the heat block 8 by the presser 9. The heat block 8 is at the position at which the work station is situated on which the well-known operations such as die bonding or wire bonding are effected.
The lead frame 7 which has undergone operations on the heat block 8 is forwarded out of the device by the clamp unit 1a which effects the forwarding operation by repeating similar cycles.
The conventional forwarding device, however, has the following disadvantage. When the lead frame 7 is forwarded over the heat block 8, the heat block 8 should be translated downward to make way for the lead frame 7 and not to interfere with the translation of the lead frame 7 thereover. However, generally, the heat block 8 must be heated to about 300.degree. C., and the mechanism for the vertical translation thereof is affected by the heat transmitted therefrom. As a result, the vertical translation mechanism is prone to failures. This results in the failure in the pressing of the lead frame, and hence, defective products are produced in the wire boding or die bonding operations.